This invention relates to introducing a hydrocarbon into the porous framework of a silicoaluminophosphate molecular sieve. More specifically, this invention is to a silicoaluminophosphate molecular sieve which contains an aromatic compound, and a method for forming said aromatic compound within the porous framework of the silicoaluminophosphate molecular sieve.
Demand for polyolefins, e.g., polyethylene and polypropylene, has been steadily increasing. It is projected that the increased demand for polyolefins will outpace the availability of raw materials, e.g., ethylene and propylene, from which polyolefins can be made.
Olefins which are used to make polyolefins have been traditionally produced from petroleum feedstocks by either catalytic or steam cracking of the petroleum. The cost of petroleum cracking has steadily increased, however, making it important to find alternative feedstock sources for olefins.
Oxygenates are a promising alternative feedstock for making olefins. Particularly promising oxygenate feedstocks are alcohols, such as methanol and ethanol, dimethyl ether, methyl ethyl ether, diethyl ether, dimethyl carbonate, and methyl formate. Many of these oxygenates can be produced by fermentation, or from synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials such as coal, recycled plastics, municipal wastes, or any appropriate organic material. Because of the wide variety of sources, oxygenates have promise as an economical source for olefin production.
One way in which olefins can be made is by catalytic conversion. In U.S. Pat. No. 4,499,327, for example, a catalytic process for converting methanol to olefins is disclosed. The catalyst used in that process contains a silicoaluminophosphate molecular sieve.
Of course, it is highly desirable to convert as much of the oxygenate feedstock as possible into as much olefin-product as possible. Various methods of doing such have been described. For example, U.S. Pat. No. 4,677,242 describes a method of increasing the amount of ethylene and propylene produced from the catalytic conversion of methanol by adding an aromatic diluent to the methanol. The catalyst that is used in the process contains a silicoaluminophosphate molecular sieve. The use of the diluent is considered to result in an increased amount of ethylene product.
U.S. Pat. No. 4,499,314 discloses a catalytic process for converting methanol to ethylene and para-xylene. The catalyst that is used is ZSM-5. Promoters are used to promote either the formation of aromatics products or olefins products. Benzene, toluene and para-xylene are preferred aromatics promoters. Ethylene, propylene and butenes are preferred olefin promoters.
There remains, nevertheless, a desire to improve the economic attractiveness of the oxygenate conversion process. Catalysts and methods to produce olefins from oxygenates are needed which increase the selectivity of the oxygenate conversion reaction, particularly to ethylene and propylene, without resorting to adding costly product enhancing promoters. In particular, it is desirable to avoid using aromatic olefin promoters to boost selectivity to ethylene and propylene.
In order to overcome the various problems associated with providing large quantities of olefin product which can ultimately be used in the manufacture of polyolefin compositions, this invention provides a crystalline silicoaluminophosphate molecular sieve comprising a porous framework structure. Within the porous framework structure there is contained a catalytically active integrated hydrocarbon co-catalyst.
In a preferred embodiment, the invention provides a method of making an integrated hydrocarbon co-catalyst, comprising preparing an silicoaluminophosphate molecular sieve having a porous framework structure and contacting said silicoaluminophosphate with a hydrocarbon at conditions effective to form at least said integrated hydrocarbon co-catalyst within the porous framework, wherein said the silicoaluminophosphate has a catalytic activity index for methanol conversion at 250xc2x0 C. of at least 2.
The integrated hydrocarbon co-catalyst is a carbonaceous material such that the silicoaluminophosphate molecular sieve containing the integrated hydrocarbon co-catalyst has a catalytic activity index for methanol conversion at 250xc2x0 C. of at least 2. The catalytic activity index is k/kini, where k is the pseudo-first order rate constant for methanol conversion at 250xc2x0 C. in the presence of the crystalline silicoaluminophosphate molecular sieve and kini is the pseudo-first order rate constant for methanol conversion at 250xc2x0 C. by injecting 1 pulse of 3 microliter of methanol in a pre-calcined crystalline silicoaluminophosphate molecular sieve activated by flowing He at 450xc2x0 C. for 1 hour.
In another embodiment, there is provided a catalyst for converting an oxygenate feedstock to an olefin product. The catalyst comprises a crystalline silicoaluminophosphate molecular sieve having a porous framework structure, and a binder, wherein the porous framework structure contains an integrated hydrocarbon co-catalyst preferably containing a single ring aromatic compound.
In preferred embodiments of the silicoaluminophosphate molecular sieve and catalyst, the aromatic composition exhibits a Solid State Nuclear Magnetic Resonance (SSNMR) spectra having a peak in the 18-22 ppm region and a peak in the 125-140 ppm region. Preferably, the aromatic composition is selected from the group consisting of alkyl substituted, single ring aromatics. Alternatively, if the intensity of the peak in the 18-22 ppm region is negligible, a peak near 128 ppm also indicates the material of this invention. Such a peak represents the presence of benzene, which has the desired effect on catalytic activity, as it rapidly reacts with the oxygenate to make alkylated single ring aromatics. More preferably, the silicoaluminophosphate molecular sieve is selected from the group consisting of SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO40, SAPO-41, SAPO-42, SAPO44, SAPO47, SAPO-56, the metal containing forms thereof, and mixtures thereof The most preferred silicoaluminophosphate molecular sieve is SAPO-34.
Also provided in this invention is a method for making an olefin product from an oxygenate feedstock. The method comprises introducing a hydrocarbon into a porous framework of a silicoaluminophosphate molecular sieve under conditions effective to form an integrated hydrocarbon co-catalyst preferably containing a single ring aromatic compound, and contacting the silicoaluminophosphate molecular sieve containing the integrated hydrocarbon co-catalyst with an oxygenate feedstock under conditions effective to convert the feedstock to an olefin product. The invention includes the olefin product made according to the described method.
In another preferred embodiment, the invention provides a method wherein the olefin product is contacted with a polyolefin-forming catalyst under conditions effective to form a polyolefin. The invention includes the polyolefin product made according to the described method.
In a more preferred embodiment, there is provided an olefin composition. The olefin composition comprises C2 to C4 hydrocarbons such as ethylene, propylene and butene.